Bores such as pipes or cylindrically shaped equipment are often submerged in a pool of water or other liquid. There is often a need to have a maintenance tool or inspection probe delivered into the submerged bore. For example, a reactor pressure vessel (RPV) of a boiling water reactor (BWR) typically has submerged bores that need to be inspected during maintenance routines. Hollow tubular jet pumps having internal bores are positioned within an annulus to provide the required reactor core water flow. The jet pump includes an upper portion, known as the inlet mixer, and a lower portion, known as the diffuser. The inlet mixer and the diffuser, due to their large size, are formed by welding a plurality of cylindrical and conical sections together. Specifically, respective ends of adjacent cylindrical sections are joined with a circumferential weld. During operation of the reactor, the circumferential weld joints may experience inter-granular stress corrosion cracking (IGSCC) and irradiation assisted stress corrosion cracking (IASCC) in weld heat affected zones which can diminish the structural integrity of the jet pump.
It is important to examine the welds of the jet pump inlet mixer and diffuser periodically to determine whether any cracking has occurred. While examinations in the annulus or region between a shroud and a pressure vessel wall can be performed, these examinations are likely to be only partial inspections due to access limitations in the annular region of the reactor. As such, the examination of the jet pump welds are often examined by an inspection tool positioned inside of the jet pump inlet mixer and jet pump diffuser. Such inspection tool performs ultrasonic and/or eddy current examinations of jet pump welds from inside the jet pump inlet mixer and diffuser in a nuclear reactor.
Typically, operational personnel located on a refuel bridge above the surface of the pool manipulate poles and other mechanical suspension devices to position a funnel to the inlet mixer of each jet pump to be inspected. For a single BWR, there can be up to 20 jet pumps and therefore 20 funnels must be attached and/or relocated during the operation. Once a funnel is positioned at the inlet of a jet pump inlet, the funnel is clamped to the inlet using another handling pole. As the inlet to the jet pumps are submerged, often up to 50 feet under the surface of the pool, the manual manipulation of these poles and the funnel is difficult and time consuming. After a funnel is attached to a jet pump inlet, a mechanical tool delivery assembly is placed in the pool. Typically, the tool delivery system is placed into the pool using an overhead crane and is then transferred to a monorail hoist on the refuel bridge. The tool delivery system is then lowered onto a head stud or top flange at the top of the open reactor pressure vessel RPV. The tool delivery system is placed between two adjacent jet pumps such that the position can be used to inspect both without having to move the tool delivery system. The tool delivery system is connected to the funnel with a locating cone and requires that one of the operators mate the cone, which is attached to a flexible arm on the lower portion of the tool delivery system, with the funnel. The arm must be manually manipulated by the operator from the refuel bridge using a rope to lower the tool delivery system until the cone is mated with the funnel.
After the tool delivery system is mated with the funnel, the inspection tool or probe is inserted into each of the funnel and the jet pump inlets to perform the inspection of the inside of the jet pump assembly. Once the first adjacent jet pump is inspected, the tool delivery system is disconnected from the first funnel and moved to the second funnel and the attachment, insertion, and inspection operations are repeated. The tool delivery system must be detached from the head stud or top flange for the first two jet pumps and manually moved to a position that is between two other jet pumps to be inspected. This manual process is repeated until all jet pumps have been inspected. Often the operator will utilize at least one submerged camera to aid in the movement, manipulation, attachment, and detachment of the submerged components.
In other systems and methods, a probe driver assembly can be located at the upper-most level of the probe outside of the jet pump diffuser. Such a probe driver assembly provides for axial movement of the inserted probe by using a take-up reel and a set of pinch wheels to raise and lower the probe head. However, such systems are difficult to position and require considerable operator involvement and still require manual placement on each jet pump. Additionally, as they require use of the full bridge, they require coordination with refueling operations and often result in additional reactor outage time.
As such, all of the current systems and methods require manual manipulation by poles to attach, move and operate submerged tools. These processes often require more than one operator. As such, current systems and methods for inspecting the inside of a submerged bore such as a nuclear reactor jet pump that can be submerged 50 feet below the surface of a water pool are difficult, time consuming, and costly. Often such tasks become a critical path item during a nuclear reactor reloading process. As such, any opportunity for reducing the required time can decrease the amount of off-line or down-time of the reactor and therefore provide significant cost savings to the reactor operator.